I actually think that was my favourite episode of Merlin since Ben Vanstone was writing in series 1. Simple premise, but so well played. I spent the whole time squeaking in delight or horror, and basically making clutchy hands going "this is so Shakespearean!" Humour, intrigue, danger, and Merlin and Arthur spending the entire time together. Tony Head bringing his A game, as usual. God, I miss him, even though I actually don't miss Uther, not even a little. And you cannot tell me that Howard Overman didn't intend that final scene to be suggestive, because the guy writes Misfits, okay? He knows what the fuck he's doing.
(On another note with this scene: THANK YOU FOR POINTING OUT ARTHUR'S 'ALL MEN ARE EQUAL' HYPOCRISY WITH HOW HE TREATS MERLIN. And thank you for having it be clear that to Arthur it's just how he expresses his undying love. And thank you for having Merlin engage in the horseplay only to realise it was a bad, bad idea. And thank you in general, really. [Especially thank you for having Arthur actually fucking listening to Merlin throughout this episode.])
The only things that didn't fill me with sparkles and joy were Gwen not being able to rescue herself and then complete disappearance, Arthur's inevitable unconsciousness during the magic reveal, and the fact that Merlin couldn't use the horn to talk to Balinor (who I think may have been less than impressed with Merlin's conduct since his death, but may also have given him confidence to talk to Arthur.) I mean, we didn't even get a line of Arthur offering and Merlin saying 'no, thanks, I don't need to look beyond the veil to know my father and I would disagree on many things'.
I believe I've said this before, but Howard Overman should be allowed to write far more of the episodes than he gets. They're almost always nine times better than everyone else's on multiple levels, retaining the goofy charm of the show but going deeper with the characters.